Condensed Consolidated Statements of Changes in Shareholders’ Equity - USD ($) $ in Thousands	Total	Common Stock	Common Stock Subscribed, Unissued	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interests
Balance at Dec. 31, 2014	$ 681,981	$ 317,199	$ 0	$ 513,672	$ (152,193)	$ 3,303
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	37,639			37,548		91
Other comprehensive income (loss)	1,253				1,417	(164)
Stock issued	10,105	10,105
Stock purchased	(8,071)	(7,974)				(97)
Advance payments	917		917
Dividends declared	(9,616)			(9,616)
Balance at Jun. 30, 2015	714,208	319,330	917	541,604	(150,776)	3,133
Balance at Dec. 31, 2015	688,146	326,482	0	548,780	(190,435)	3,319
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	40,791			40,680		111
Other comprehensive income (loss)	10,694				10,443	251
Stock issued	11,452	11,452
Stock purchased	(5,856)	(5,503)				(353)
Advance payments	511		511
Dividends declared	(9,977)			(9,977)
Balance at Jun. 30, 2016	$ 735,761	$ 332,431	$ 511	$ 579,483	$ (179,992)	$ 3,328